the specialist in diseases of the eye unfolded a plan of tre

B
which he was sure would retore the patient's vision是定语从句,其中he was sure是插入语.插入语要放在从句的中间,不能放在从句的前面,排除A、C.
把he was sure拿掉后,就是which would retore the patient's vision,从中可以很明显地看出,which在从句中作主语,是不能省略的.排除D.